This application is based on application No. JP 2000-000793 filed in Japan, the contents of which is hereby incorporated by reference.
1. Field of the Invention
The present invention pertains to an improved liquid material supply device that causes a liquid material (such as ink, for example) to be carried on the continuous outer circumferential surface (liquid material carrying surface) of a continuous carrier (such as a roller or a belt, for example), as well as to an image forming apparatus incorporating such liquid material supply device.
2. Description of the Related Art
Among various types of liquid ink supply devices are those that use a blade to cause the ink adhering to the outer circumferential surface of a rotating roller to become a thin uniform-thickness layer, and transfer this thin layer of ink to an image (comprising convex areas, or a latent image) carried on a plate, image carrier, etc.
In an ink supply device of this type, a prescribed pressure is applied to the blade such that it is in pressure contact with the outer circumferential surface of the rotating roller. The excess ink adhering to the roller is removed by the blade when the ink passes through the area of contact between the blade and the roller. As a result, a uniform thin layer of ink is formed. In addition, the thickness of the ink layer may be varied by adjusting the pressure applied to the blade that is in contact with the roller.
FIG. 11 shows a conventional ink supply device 1 using a blade as described above. This ink supply device 1 includes a container (developer container) 2. An ink cartridge 4 is located in the housing of the container 2 such that it may be removed. Ink 6 is supplied from the cartridge 4 to the container 2 such that the depth of the ink 6 is maintained at a prescribed level in the container 2. A roller (developing roller) 10, which has a shaft 8 that runs parallel to the surface of the ink 6 and extends in the direction perpendicular to the sheet, is located in the upper area of the container 2 such that the bottom of the roller is below the ink surface. The shaft 8 is connected to a motor 12, so that the roller 10 rotates in the direction of an arrow 13 in the drawing as the motor 12 rotates. A regulating blade 16, which comprises a plate-shaped elastic member supported by a pressing member 14, is located downstream from the area of the roller submerged in the ink 6 in terms of the roller rotational direction 13. This regulating blade 16 protrudes essentially tangentially to the roller 10 and in the downstream direction of the rotation of the roller 10, such that it is in contact with the roller 10 under a prescribed pressure. In addition, an image carrier (image carrying roller) 22, which has a shaft 20 that is parallel to the surface of the ink 6 and extends in the direction perpendicular to the sheet, and carries a latent image in accordance with image information, is located above and near the roller 10. The shaft 20 is connected to a motor 24, and the image carrier 22 rotates in the direction of the arrow 25 of the drawings as the motor 24 rotates.
The operation of the ink supply device 1 will be explained below with reference to FIG. 11. When the roller 10 rotates via the motor 12, the ink 6 adhering to the surface of the roller 10 reaches the regulating blade 16 as it is carried on the roller 10 as the roller 10 rotates. Here, excess ink 6 is removed by the regulating blade 16 through the receipt of a prescribed pressure therefrom. A uniform thin layer of ink 6 having a desired thickness (several xcexcm to several tens of xcexcm) is formed on the surface of the roller 10 in accordance with the pressure from the regulating blade. The thin layer of ink 6 is then transferred to the image carrier 22 in the transfer area 26. For the method by which to transfer the ink 6 to the image carrier 22 from the roller 10, either a contact method or a non-contact method may be used.
In the ink supply device 1 described above, where the opening 28 (the area indicated by dotted lines in the drawing) through which the interior of the container 2 is exposed to the outside atmosphere is large, the amount of solvent (i.e., water in the case of a water-based ink) of the ink 6 in the container 2 that evaporates and escapes through the opening 28 is large, and consequently, the viscosity of the ink 6 increases. If the container 2 were completely closed off, the water component of the ink 6 would be maintained in equilibrium between the ink 6 housed in the container 2 and the remaining space in the container 2, and therefore the viscosity of the ink 6 would change very little. However, in actuality, the container 2 is never completely closed during development due to the mechanical construction of the device. When the viscosity of the ink increases, an ink layer that is thicker than the desired thickness is formed on the roller 10. Such an increase in the ink layer thickness increases the amount of ink transferred to the image carrier 22, and in turn, image failure when an image is formed on the sheet using this ink (such as the so-called cockling in which the sheet warps as a result of shrinking due to absorbed ink, resulting in a wavy sheet surface, for example) as well as ink bleed-through. (In this application, xe2x80x98the outside atmospherexe2x80x99 refers to the atmosphere that exists outside the opening 28 of the container 2, and is distinguished from the gas that exists inside the opening 28 of the container 2).
The present invention was created in view of the situation described above, and the object thereof is to provide an improved ink supply device. In other words, an object of the present invention is to provide an ink supply device that can supply ink under stable conditions. More particularly, an object of the present invention is to provide an ink supply device that prevents the solvent, which is the main ingredient of the ink inside the developer container, from evaporating and escaping from the container, in order to maintain the ink viscosity at an essentially fixed level, and that consequently forms a layer of ink having an essentially uniform thickness on the surface of a liquid carrier such as a roller 10.
In order to attain this and other objects, the liquid material (ink) supply device according to one aspect of the present invention has a rotational shaft; a liquid material carrier having a continuous liquid material carrying surface around the rotational shaft; a motor that causes the liquid material carrier to rotate in a prescribed direction around the rotational shaft; and a container that houses a liquid material such that a part of the liquid material carrying surface may be submerged in the liquid material, so that the liquid material may be supplied onto the liquid material carrying surface, and the top part of which is open, wherein the liquid material supplied onto the liquid material carrying surface is conveyed to the transfer area through the rotation of the liquid material carrier that occurs based on the rotation of the motor, and is supplied to the liquid material receiving member in the transfer area. The liquid material supply device further has a liquid material supply mode in which the liquid material is supplied from the liquid material carrier to the liquid material receiving member, and a liquid material non-supply mode in which the liquid material is essentially removed from the liquid material carrier.
In this liquid material supply device, according to one aspect of the present invention, a part of the liquid material carrier is located outside the opening of the container, and the liquid material is supplied from the liquid material carrier to the liquid material receiving member using one area of the above part of the liquid material carrier, and the opening area A and the liquid material surface area B defined below satisfy the relationship (A/B) less than 1 when the liquid material supply mode or the liquid material non-supply mode is present.
(1) When Liquid Material Supply Mode is Present
Opening area A: The area of the opening of the container
Liquid material surface area B: The sum of the area of the liquid surface other than the part thereof in which the liquid material carrier is submerged, and the area of the liquid material surface carried on the liquid material carrier above the liquid surface.
(2) When Liquid Material Non-Supply Mode is Present
Opening area A: The area of the opening of the container from which the area of the part thereof taken up by the liquid material carrier is subtracted.
Liquid material surface area B: The area of the liquid surface other than the part thereof in which the liquid material carrier is submerged.
According to another aspect of the present invention, the liquid material carrier is located inside the container while the liquid material receiving member is located outside the container, the liquid material is supplied to the liquid material receiving member from the liquid material carrier via the opening of the container, and the opening area A and the liquid material surface area B defined below satisfy the relationship (A/B) less than 1 when the liquid material supply mode or liquid material non-supply mode is present.
(1) When Liquid Material Supply Mode is Present
Opening area A: The area of the opening of the container
Liquid material surface area B: The sum of the area of the liquid surface other than the part thereof in which the liquid material carrier is submerged, and the area of the liquid material surface carried on the liquid material carrier above the liquid surface.
(2) When Liquid Material Non-Supply Mode is Present
Opening area A: The area of the opening of the container
Liquid material surface area B: The area of the liquid surface other than the part thereof in which the liquid material carrier is submerged.
Furthermore, according to yet another aspect of the present invention, the liquid material carrier is located inside the container while a part of the liquid material receiving member is located inside the opening of the container, the liquid material is supplied to the liquid material receiving member from the liquid material carrier using an area of the above part of the liquid material receiving member, and the opening area A and the liquid material surface area B defined below satisfy the relationship (A/B) less than 0.3 when the liquid material supply mode or the liquid material non-supply mode is present.
(1) When Liquid Material Supply Mode is Present
Opening area A: The area of the opening of the container from which the area of the part thereof taken up by the liquid material receiving member is subtracted.
Liquid material surface area B: The sum of the area of the liquid surface other than the part thereof in which the liquid material carrier is submerged, and the area of the liquid material surface carried on the liquid material carrier above the liquid surface.
(2) When Liquid Material Non-Supply Mode is Present
Opening area A: The area of the opening of the container from which the area of the part thereof taken up by the liquid material receiving member is subtracted.
Liquid material surface area B: The area of the liquid surface other than the part thereof in which the liquid material carrier is submerged.